1. Field of the Invention
The present invention relates to a process for the oxidation of hydrocarbons that uses molecular oxygen as the oxidant and more particularly to a catalytic cycle, driven by an artificial photosynthesis system, which mimics the cytochrome P.sub.450 reaction to oxidize alkanes and olefins. The Government has rights in this invention pursuant to Contract No. DE-AC04-76DP00789 awarded by the U.S. Department of Energy to AT&T Technologies, Inc.
2. Description of Related Art
Cytochrome P.sub.450 is a typical mono-oxygenase, inserting one oxygen atom of O.sub.2 into a substrate molecule and using the other to form H.sub. O. Any catalyst which mimics cytochrome P.sub.450 is a biomimetic oxidation catalyst; it mimics the biological oxidation reactions of Cytochrome P.sub.450. Visible light has been used to activate O.sub.2 for room-temperature conversion of alkanes to alcohols. One of the drawback of a biomimetic approach to oxidation of nycrocarbons ls that a strong reductant is required at two stages in the catalytic cycle using an Fe porphyrin. When molecular oxygen is used as the oxidant, as is the case for cytochrome P.sub.450, the reductant reduces iron from Fe.sup.III or Fe.sup.II so that O.sub.2 can bind. Then, another reductant molecule is expended to break the ) O-O bond to provide the reactive Fe-O intermediate. Strong reductants such as Zn, NaBH.sub.4, and H.sub.2 have been used for this purpose. These reductants are valuable in themselves and must be replenished to sustain the hydrocarbon-oxidation reaction.
Previously, a system which mimics biological photosynthesis has been disclosed in U.S. Pat. No. 4,568,435 to Shelnutt. This artificial photosynthesis system uses a tin porphyrin as a light absorbing pigment to produce reducing equivalents.
Previously, a great variety of alkane and olefin oxidation systems that mimic biological oxidation of hydrocarbons by cytochrome P.sub.450 have been reported. Most use an iron, manganese, or ruthenium porphyrin as the analog of the heme (iron porphyrin) functional group of the enzyme. Ortiz de Montellano, P.R., ed."Cytochrome P-450, Structure, Mechanism, and Biochemistry" (Plenum: New York) 1986; Guengerich, F.P.; Macdonald, T.L., Acc. Chem. Res. 1984, 17,9; Groves, J.T.; Nemo, T.E. et al., J. Am. Chem. Soc. 1979, 101,1032. In the great majority of these chemistries a single oxygen atom donor, such as iodosylbenzene or hypochlorite, is used as the oxidant rather than molecular oxygen. However, Karasevich et al., Institute of Chemical Physics, U.S.S.R. Academy of Sciences, J. Chem. Soc., Chem. Commun. 1987, 731-732 discloses that cytochrome P.sub.450 activitation of dioxygen on iron porphyrin as a catalytic center can be accomplished using of Zn(Hg) as a reducing agent, methylviologen as a mediator and acetic anhydride as an acylating agent. Nevertheless, the Russian hydrocarbon-oxidation system employed a non-newable reductant and, hence, the yield was low.